CN108491427B - PDF tile map and manufacturing method thereof - Google Patents

PDF tile map and manufacturing method thereof Download PDF

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CN108491427B
CN108491427B CN201810128566.0A CN201810128566A CN108491427B CN 108491427 B CN108491427 B CN 108491427B CN 201810128566 A CN201810128566 A CN 201810128566A CN 108491427 B CN108491427 B CN 108491427B
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map
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coordinates
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周校东
黄利民
何列松
谢鹏
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61540 Troops of PLA
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Abstract

The invention relates to a PDF tile map and a manufacturing method thereof. The PDF tile map adopts a tile pyramid model to store graphic information with map expression and interactive geographic information in a PDF format, has all the characteristics of the PDF map, and mainly comprises the following steps: firstly, a PDF tile map pyramid model is established, then other projected PDF maps are transformed into a Web mercator projection PDF map through projection, finally, the Web mercator projection PDF map is cut based on the PDF tile map pyramid model, the PDF tile maps with the same tile coordinates are spliced, and finally the PDF tile map is obtained. The PDF tile map disclosed by the invention can provide a multi-level grid tile map service, has a geographic element interaction capacity, seamlessly organizes and manages the PDF map through tiling treatment and provides various map visualization services, so that the use of the PDF map is not limited by the map format.

Description

PDF tile map and manufacturing method thereof
Technical Field
The invention belongs to the technical field of PDF maps, and particularly relates to a PDF tile map and a manufacturing method thereof.
Background
Pdf (portable document format) is a widely used electronic document format developed and designed by Adobe corporation, and its obvious feature is that the same display effect can be maintained on different devices. GeoPDF, a registered trademark of terrargo technology corporation, a subsidiary of Layton Graphics, is rapidly becoming the first format for map distribution, and the OGC organization has made GeoPDF a recommended map coding standard. At present, the use of the GeoPDF is based on a single image, and a user can only be limited to a GeoPDF file when browsing the GeoPDF, which is a great defect when using the GeoPDF. The PDF map is an important result of domestic research on Geospatial PDF, and the manufacture and the use of the PDF map are similar to those of GeoPDF.
The map tile technology is a main approach for solving the internet map service so far, and currently, mainstream network maps issue map pictures on clients in a grid tile mode. Considering that grid tiles have the defects of huge data amount, lack of interaction capacity for geographic elements and the like, the research of vector data-based network maps gradually becomes a hot problem, and the "vector tile" maps appear successively. In general, the vector tile map uses a graphic expression mode to quickly obtain a symbolic map by establishing a symbolic mapping mechanism on the basis of geographic elements, but the effect of the symbolic map is far less than that of a standard map which is edited and used for publishing.
Disclosure of Invention
Aiming at the defects or shortcomings in the prior art, the invention aims to provide a PDF tile map and a manufacturing method thereof, which are used for expanding the use modes of GeoPDF and PDF maps and making up the defects that the current grid tiles have huge data total amount and lack of geographic element interaction capacity and vector tiles lack of map expression capacity. The PDF tile map adopts a tile pyramid model to store the graphic information with map expression and interactive geographic information in a PDF format, and has all the characteristics of the PDF map. The PDF tile map making method mainly comprises the following steps: firstly, a PDF tile map pyramid model is established, then other projected PDF maps are transformed into a Web mercator projected PDF map through projection, finally, the Web mercator projected PDF map is cut based on the tile pyramid model, the PDF tile maps with the same tile coordinates are spliced, and finally the PDF tile map is obtained.
The technical scheme adopted by the invention is as follows:
PDF tile map, its characterized in that:
the PDF tile map adopts a tile pyramid model to store graphic information with map expression and interactive geographic information in a PDF format, has all characteristics of the PDF map, can provide multi-level grid tile map service, has geographic element interaction capacity, seamlessly organizes and manages the PDF map through tiling processing and provides various map visualization services, so that the use of the PDF map is not limited by map sheets any more.
The method for manufacturing the PDF tile map is characterized in that:
the manufacturing method of the PDF tile map is realized by the following steps:
the method comprises the steps of adopting a tile pyramid model to store a PDF map in a blocking mode in a PDF format, firstly establishing the PDF tile map pyramid model, then converting other projected PDF maps into a Web mercator projected PDF map through projection, finally cutting the Web mercator projected PDF map based on the PDF tile map pyramid model, splicing the PDF tile maps with the same tile coordinates, and finally obtaining the PDF tile map.
The method specifically comprises the following steps:
step 1: establishing a PDF tile map pyramid model, which specifically comprises the following steps:
(1) establishing a Web mercator projection coordinate transformation object;
(2) dividing the pyramid level of the PDF tile map, and converting the Web mercator projection coordinates into user coordinates of the PDF tile map corresponding to tile coordinates under a certain level Z in the pyramid level;
step 2: the PDF map projective transformation is a Web mercator projection, and specifically comprises the following steps:
(1) analyzing the Gaussian projection PDF map file by using a PDF map analyzer to obtain a Gaussian projection PDF map object;
(2) establishing a coordinate transformation model of the Gaussian projection PDF map to the Web mercator projection PDF map;
(3) extracting all graphic objects in a PDF map page, and performing coordinate transformation on point coordinates in the graphic objects by using a coordinate transformation model;
(4) setting page size, map projection parameters and transformation matrix parameters, and storing a Web mercator projection PDF map file.
And step 3: cutting the Web mercator projection PDF map based on the PDF tile map pyramid model, and specifically comprises the following steps:
(1) obtaining a map scale and a map frame range by using a PDF map object, and calculating and returning a tile coordinate list covered by the map frame range;
(2) based on the tile coordinate list, cutting the graphic objects in the PDF map page by using a PDF page cutting technology;
and 4, step 4: and acquiring and splicing PDF tile maps with the same tile coordinates obtained by cutting adjacent map sheets.
The step 1(1) is to establish a Web mercator projection coordinate transformation object, and is specifically realized by the following steps:
the PDF tile map pyramid model takes a square area, so, when the Mexico Kanto projection is adopted, the earth is regarded as a sphere, the equator is taken as a standard latitude line, the initial meridian is taken as a central meridian, the intersection point of the two is the origin of coordinates, the east is the X-axis forward direction, the north is the Y-axis forward direction, and the projection formula is shown as formula 1:
Figure GDA0001654525460000041
wherein:
r6378137 meters, i.e. radius of the earth;
λ -longitude in radians;
Figure GDA0001654525460000042
-latitude in radians;
the step 1(2) is to divide the pyramid level of the PDF tile map, and transform the Web mercator projection coordinates into user coordinates of the PDF tile map corresponding to tile coordinates at a certain level Z in the pyramid level, and is specifically realized by the following steps:
the PDF tile map adopts Web mercator projection, the map range is a square area, and the side length is as follows: 40075016.686 meters, latitude range: -85.05 ° to 85.05 °, longitude range: -180 ° to 180 °;
the tile blocking specifically comprises:
dividing map range into 4 equal parts9The block is used as the level 1 of the PDF tile map, and the corresponding map scale is 1:100 ten thousand;
2, each block of the 1 st stage is equally divided into 42Block, as level 2 of PDF tile map, corresponding map scale of1:25 ten thousand;
3 equally dividing each block of the 2 nd level into 43The block is used as the 3 rd level of the PDF tile map, and the corresponding map scale is 1:5 ten thousand;
fourthly, each block of the 3 rd level is equally divided into 42The block is used as the 4 th level of the PDF tile map, and the corresponding map scale is 1:1 ten thousand;
equally dividing each block of the 4 th level into 42A block, as level 5 of the PDF tile map, with a corresponding map scale of 1:2 k;
the tile coordinate origin of the PDF tile map is at a position where the longitude and latitude are both 0, with the lower left corner of the PDF tile as a reference point, tile coordinates (Z, X, Y), where: z is PDF tile map level, 1-5 levels in total; x, Y are integers, starting with 0; x is horizontal, Y is vertical, the origin of coordinates is positive upwards and rightwards, and negative downwards and leftwards, namely the east longitude X takes a positive value, the west longitude X takes a negative value, the north latitude Y takes a positive value, and the south latitude Y takes a negative value;
PDF tile map coordinate transformation: the longitude and latitude coordinates and the Web mercator projection coordinates are directly transformed by a formula 1 and are irrelevant to the level of the PDF tile map; the Web mercator projection coordinates are converted into tile coordinates and user coordinates at a certain PDF tile map level;
the Web mercator projection coordinates (X, Y) are transformed into tile coordinates (X, Y) at a certain level Z, as shown in equation 2:
Figure GDA0001654525460000061
in the formula, R is the earth radius, d is the tile side length, and INT represents rounding the numerical value in brackets, namely, rounding off the part behind a decimal point;
the Web mercator projection coordinates (X, Y) are transformed into user coordinates (U) of the PDF tile map corresponding to tile coordinates (X, Y) at a certain level Zx,Uy) As shown in equation 3:
Figure GDA0001654525460000062
in the formula (I), the compound is shown in the specification,
Figure GDA0001654525460000063
k is the map scale denominator at a certain level Z.
The step 2(1) is to analyze the gaussian projection PDF map file by using a PDF map analyzer to obtain a gaussian projection PDF map object, and is specifically realized by the following steps:
the PDF map object comprises a PDF document structure tree object and a PDF map space reference object, the PDF document structure tree mainly comprises PDF map page nodes, and the PDF map space reference mainly realizes the purpose of converting the user coordinates of the graphic object in the page into projection coordinates and longitude and latitude coordinates;
the step 2(2) is to establish a coordinate transformation model of the gaussian projection PDF map to the Web mercator projection PDF map, and is specifically realized by the following steps:
for gaussian projection PDF maps, with PDF map objects: firstly, acquiring a Gaussian projection PDF map scale of 1: K; acquiring geographical longitude and latitude of map range of Gaussian projection PDF map, namely longitude and latitude coordinates of left lower corner of inner outline
Figure GDA0001654525460000064
Longitude and latitude coordinates of upper right corner
Figure GDA0001654525460000075
Thirdly, the longitude and latitude coordinates are calculated by the formula 1
Figure GDA0001654525460000076
Conversion to Web mercator projection coordinates (x)1,y1)、(x2,y2)；
In the process of transforming the Gaussian projection PDF map into the Web mercator projection PDF map, eliminating the graphic object outside the inner outline, only transforming the graphic object within the map breadth range, and taking the inner outline rectangle as the page rectangle of the transformed Web mercator projection PDF map; establishing a user coordinate transformation formula for projecting the PDF map to the Web mercator by the Web mercator projection coordinates, wherein the user coordinate transformation formula is shown as a formula 4:
Figure GDA0001654525460000071
in the formula (I), the compound is shown in the specification,
Figure GDA0001654525460000072
k is a map scale denominator;
the width of the page rectangle of the Web mercator projection PDF map is as follows:
Figure GDA0001654525460000073
the height is:
Figure GDA0001654525460000074
the step 2(3) extracts all the graphic objects in the PDF map page, and performs coordinate transformation on the point coordinates in the graphic objects by using a coordinate transformation model, which is specifically realized by the following steps:
traversing all the graphic objects in the content stream under the page node, acquiring the user coordinates of all the points of each graphic object aiming at each graphic object, and performing the following processing:
converting user coordinates into longitude and latitude coordinates by using PDF map space reference;
converting the longitude and latitude coordinates into Web mercator projection coordinates;
thirdly, transforming the Web mercator projection coordinate into a user coordinate after coordinate transformation;
replacing the user coordinate before coordinate transformation with the user coordinate after point coordinate transformation in the graphic object;
updating the content flow of the PDF map page when the point coordinates of all the graphic objects in the page are converted;
the step 2(4) is to set the page size, the map projection parameters and the transformation matrix parameters, and store the Web mercator projection PDF map file, and is specifically realized by the following steps:
setting the size of a Web mercator projection PDF map Page (Page) and the width as follows:
Figure GDA0001654525460000081
the height is:
Figure GDA0001654525460000082
secondly, setting map projection parameters in the space reference nodes under the page as Web mercator projection, wherein the specific parameter table is as follows:
web mercator projection parameter table
Figure GDA0001654525460000083
Thirdly, setting transformation matrix parameters [ a b c d e f ] in space reference nodes under the page]Is [ s 00 s x ]1y1]；
And fourthly, updating the PDF document structure tree, and saving the PDF map object into the new PDF file to obtain the Web mercator projection PDF map file.
The step 3(1) is to obtain a map scale and a map range by using the PDF map object, calculate and return a tile coordinate list covered by the map range, and is specifically realized by the following steps:
acquiring a map scale K and PDF tile map level of a Web mercator projection PDF map;
obtaining the projection coordinates of the Web mercator in the picture range of the PDF map projected by the Web mercator, and the lower left corner point (x)LB,yLB) Right upper corner point (x)RT,yRT)；
Calculating (x)LB,yLB)、(xRT,yRT) Tile coordinates (X) at acquisition levelLB,YLB)、(XRT,YRT)；
Fourthly, returning the tile coordinate list { (X, Y) | XLB≤X≤XRT，YLB≤Y≤YRT}；
The step 3(2) is to perform cutting processing on the graphic object in the PDF map page by using a PDF page cutting technology based on the tile coordinate list, and is specifically realized by the following steps:
measuringCalculating the user coordinates of the tile rectangle corresponding to the tile coordinates (X, Y) at the level Z in the PDF map page: lower left corner (Ux)1,Uy1) Right upper corner point (Ux)2,Uy2) The tile rectangle is expanded by 0.567 to obtain a clipping rectangle R (R)left，Rbottom，Rright，Rtop) For graphic objects within a PDF map page: if the circumscribed rectangle is outside the cutting rectangle, no processing is carried out; if the bounding rectangle is within or intersects the cropping rectangle, copying the graphical object into a PDF map page in a PDF tiled map object and transforming the point coordinates in the graphical object to the lower left corner point (Ux) of the tiled rectangle1，Uy1) If the graphic object is associated with the attribute information, adding the attribute information associated with the graphic object into a PDF map page in the PDF tile map object, and simultaneously associating the graphic object in the PDF map page in the PDF tile map object;
if the graphic object is a path object and the attribute information is not associated, preferably, when the circumscribed rectangle and the clipping rectangle are intersected, performing vector clipping processing on the path by using the clipping rectangle: if the path only consists of a plurality of straight line segments, namely a broken line or a polygon, the broken line cutting and the polygon cutting are realized by adopting a classical algorithm; if the path is composed of the cubic bezier curve or is composed of a straight line segment and the cubic bezier curve in a mixed mode, the path cutting processing is carried out by taking the cubic bezier curve as a unit under the condition that the intersection point of the cubic bezier curve and the cutting rectangle is not specifically calculated.
Step 4, obtaining and splicing the PDF tile maps with the same tile coordinates obtained by cutting adjacent map sheets, which is specifically realized by the following steps:
extracting PDF tile map files with the same tile coordinates under the same map level, wherein the number of the files is more than 1, and storing the files into a file list;
analyzing a first PDF tile map file in the file list by using a PDF map analyzer to obtain a target PDF map object;
analyzing the next PDF tile map file in the file list by using a PDF map analyzer to obtain a source PDF map object;
acquiring all the graphic objects by utilizing the page objects of the source PDF map object, sequentially copying each graphic object into the page object of the target PDF map object, copying the associated attribute information into the page object of the target PDF map object if the graphic object has the associated attribute information, and deleting the source PDF map object and the corresponding PDF tile map file after the copying is successful;
and fifthly, if the number of the files in the file list is larger than 2, repeating the third step and the fourth step, updating the page object of the target PDF map object, and outputting and replacing the PDF file corresponding to the target PDF map object by using the target PDF map object to obtain the spliced PDF tile map.
The invention has the following advantages:
the PDF tile map disclosed by the invention can provide a multi-level grid tile map service, has a geographic element interaction capability, seamlessly organizes and manages the PDF map through tiling processing, and provides a plurality of map visual services, so that the use of the PDF map is not limited by the map, the use mode of the PDF map is expanded, and the user experience is greatly enriched and promoted. The PDF tile map manufactured by the method only needs to establish one layer of PDF tile map on the same scale, can provide multi-level grid tiles by setting the zoom factor, has the grid tile network map service capability, greatly reduces the data volume and has the geographic element interaction capability compared with the grid tiles, and can provide higher-quality map visualization service compared with a vector tile map.
Drawings
FIG. 1 is a flow chart of a PDF tile map and a method for making the same according to the present invention;
FIG. 2 is a square area range of a PDF tile map in an embodiment of the present invention;
FIG. 3 is a schematic diagram of PDF tile coordinates at a map level according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of coordinate transformation of a PDF tile map according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating exemplary clipping of polylines and polygons in an embodiment of the present invention;
FIG. 6 is a diagram illustrating an exemplary clipping of a path containing cubic bezier curves in an embodiment of the present invention.
FIG. 7 is a schematic diagram of splicing PDF tile maps with the same tile coordinates according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific embodiments.
The invention relates to a PDF tile map and a manufacturing method thereof, which adopts a strategy of storing the PDF map in blocks in a PDF format, establishes a PDF tile map pyramid model, transforms other projected PDF maps into a Web mercator projection PDF map through projection, cuts the Web mercator projection PDF map based on the PDF tile map pyramid model, splices the PDF tile maps with the same tile coordinates, and finally obtains the PDF tile map, as shown in FIG. 1, the method comprises the following steps:
step 1: and establishing a PDF tile map pyramid model.
The pyramid model is a multi-scale model, and can be constructed by adopting a multiplying power relation while maintaining data continuity, so that functions of stepless zooming, seamless roaming and the like of the PDF tile map are realized. In the whole process of building the pyramid model of the PDF tile map, the size of tiles, the latitude and longitude range, the layer number of the pyramid model and the corresponding map scale of the PDF tile map need to be determined. The specific establishment process is as follows:
(1) and establishing a Web mercator projection coordinate transformation object.
In order to facilitate calculation and determine partitioning and index coding of the PDF tile map, a square area is taken as the PDF tile map pyramid model. Thus, when using the mercator projection, the earth is considered to be a sphere, rather than an ellipsoid, i.e., the Web mercator projection. The Web mercator projection takes the equator as a standard weft, the initial meridian as a central meridian, the intersection point of the two is a coordinate origin, the east is the X-axis forward direction, the north is the Y-axis forward direction, and the projection formula is shown as formula 1:
Figure GDA0001654525460000121
wherein: r6378137 m (earth radius), λ -longitude,
Figure GDA0001654525460000122
Latitude (in radians).
(2) And dividing the pyramid level of the PDF tile map.
The PDF tile map adopts Web mercator projection, the map range is a square area, and the side length is as follows: 40075016.686 meters, latitude range: -85.05 ° to 85.05 °, longitude range: 180 ° to 180 °, as shown in fig. 2.
TABLE 1 PDF Tile map pyramid level Table
Figure GDA0001654525460000131
The PDF tile map pyramid rule is shown in table 1, and mainly includes map data of five scales of 1:100 ten, 1:25 ten, 1:5 ten, 1:1 ten and 1:2 thousand, and the tile blocking specific method is as follows:
dividing map range into 4 equal parts9The block is used as the level 1 of the PDF tile map, and the corresponding map scale is 1:100 ten thousand;
2, each block of the 1 st stage is equally divided into 42The block is used as the level 2 of the PDF tile map, and the corresponding map scale is 1:25 ten thousand;
3 equally dividing each block of the 2 nd level into 43The block is used as the 3 rd level of the PDF tile map, and the corresponding map scale is 1:5 ten thousand;
fourthly, each block of the 3 rd level is equally divided into 42The block is used as the 4 th level of the PDF tile map, and the corresponding map scale is 1:1 ten thousand;
equally dividing each block of the 4 th level into 42The block, as level 5 of the PDF tile map, corresponds to a map scale of 1:2 thousand.
The tile coordinate origin of the PDF tile map is at a position where the longitude and latitude are both 0, with the lower left corner of the PDF tile as a reference point, tile coordinates (Z, X, Y), where: z is PDF tile map level, 1-5 levels in total; x, Y is an integer starting from 0. If tile coordinates (X, Y) at a certain level Z are shown in fig. 3, X is horizontal, Y is vertical, the origin of coordinates is positive upward and rightward, and negative downward and leftward, i.e., east longitude X takes a positive value, west longitude X takes a negative value, north latitude Y takes a positive value, and south latitude Y takes a negative value.
The PDF tile map coordinate transformation is shown in FIG. 4, where: the longitude and latitude coordinates and the Web mercator projection coordinates can be directly transformed by a formula 1 and are irrelevant to the level of the PDF tile map; the Web mercator projection coordinates may be transformed into tile coordinates and user coordinates at a certain PDF tile map level.
The Web mercator projection coordinates (X, Y) are transformed into tile coordinates (X, Y) at a certain level Z, as shown in equation 2:
Figure GDA0001654525460000141
where R is the earth's radius, d is the tile edge length, and INT indicates rounding the parenthesized value, i.e., rounding off the part behind the decimal point.
The Web mercator projection coordinates (X, Y) are transformed into user coordinates (U) of the PDF tile map corresponding to tile coordinates (X, Y) at a certain level Zx,Uy) As shown in equation 3:
Figure GDA0001654525460000142
in the formula (I), the compound is shown in the specification,
Figure GDA0001654525460000143
k is the scale denominator of the map at a certain level Z (e.g., when Z is 3, K is 50000), and d is the same as formula 2.
Step 2: the PDF map projection is transformed into a Web mercator projection.
The PDF tile map manufacturing data source is a PDF map generated by a national basic scale topographic map, the national basic scale topographic map adopts two map projections, the topographic map with the scale larger than or equal to 1:50 adopts Gauss-Krigger projection, and the topographic map with the scale of 1:100 adopts double-standard latitude line equiangular cone projection. In the process of manufacturing the PDF tile map, firstly, the PDF map needs to be subjected to projection transformation processing, namely, the map projection of the PDF map is projected by a non-Web mercator, and is transformed into a Web mercator projection by using a PDF map projection transformation method.
The PDF map projection transformation method mainly performs coordinate projection transformation on point coordinates of all graphic objects in a PDF map page point by point so as to obtain a PDF map after projection transformation. In order to better describe the PDF map projection transformation method, the invention takes the example that the Gaussian projection PDF map is transformed into the Web mercator projection PDF map, and the concrete transformation process is as follows:
(1) and analyzing the Gaussian projection PDF map file by using a PDF map analyzer to obtain a Gaussian projection PDF map object.
The PDF map parser can be implemented by modifying various open-source PDF parsing libraries (such as PDFium, MuPDF, SumatraPDF, PDFLib and the like), and each PDF map file corresponds to one PDF map object after being parsed. The PDF map object comprises a PDF document structure tree object and a PDF map space reference object, the PDF document structure tree mainly comprises PDF map Page (Page) nodes, and the PDF map space reference mainly realizes that the user coordinates of the graphic object in the Page are converted into projection coordinates and longitude and latitude coordinates.
(2) And establishing a coordinate transformation model of the Gaussian projection PDF map to the Web mercator projection PDF map.
For gaussian projection PDF maps, with PDF map objects: firstly, acquiring a map scale of the Gaussian projection PDF to be 1: K (if the map scale is 1:5 ten thousand, K is 50000); acquiring geographical longitude and latitude of map range of Gaussian projection PDF map, namely longitude and latitude coordinates of left lower corner of inner outline
Figure GDA0001654525460000161
Longitude and latitude coordinates of upper right corner
Figure GDA0001654525460000162
Utilizing formula 1 to divide longitude and latitudeDegree coordinate
Figure GDA0001654525460000163
Conversion to Web mercator projection coordinates (x)1,y1)、(x2,y2)。
In the process of converting the Gaussian projection PDF map into the Web mercator projection PDF map, the graphic object outside the inner outline is omitted, only the graphic object in the map breadth range is converted, and the inner outline rectangle is used as the page rectangle of the converted Web mercator projection PDF map. Establishing a user coordinate transformation formula for projecting the PDF map to the Web mercator by the Web mercator projection coordinates, wherein the user coordinate transformation formula is shown as a formula 4:
Figure GDA0001654525460000164
in the formula (I), the compound is shown in the specification,
Figure GDA0001654525460000165
k is the scale denominator of the map.
The width of the page rectangle of the Web mercator projection PDF map is as follows:
Figure GDA0001654525460000166
the height is:
Figure GDA0001654525460000167
(3) and extracting all the graphic objects in the PDF map page, and performing coordinate transformation on the point coordinates in the graphic objects by using a coordinate transformation model.
Traversing all the graphic objects in the content stream (Contents) under the page node, and aiming at each graphic object, acquiring the user coordinates of all the points of the graphic object, and performing the following processing:
converting user coordinates into longitude and latitude coordinates by using PDF map space reference;
secondly, transforming the longitude and latitude coordinates into Web mercator projection coordinates by using a formula 1;
thirdly, transforming the Web mercator projection coordinate into a user coordinate after coordinate transformation by using a formula 4;
and replacing the user coordinate before the coordinate transformation with the user coordinate after the point coordinate transformation in the graphic object.
And when the point coordinates of all the graphic objects in the page are converted, updating the content flow of the PDF map page.
(4) Setting page size, map projection parameters and transformation matrix parameters, and storing a Web mercator projection PDF map file, wherein the specific process comprises the following steps:
setting the size of a Web mercator projection PDF map Page (Page) and the width as follows:
Figure GDA0001654525460000171
the height is:
Figure GDA0001654525460000172
setting map Projection (Projection) parameters in a spatial reference node (LGIDict) under a page as Web mercator Projection, as shown in Table 2;
third, setting parameters [ a b c d e f ] of transformation matrix (CTM) in spatial reference node (LGIDick) under page]Is [ s 00 s x ]1 y1]；
And fourthly, updating the PDF document structure tree, and saving the PDF map object into the new PDF file to obtain the Web mercator projection PDF map file.
TABLE 2 Web Mocha support projection parameters Table
Figure GDA0001654525460000173
And step 3: and cutting the Web mercator projection PDF map based on the PDF tile map pyramid model.
The graphical objects in the PDF map page comprise two parts, wherein one part of the graphical objects is specially used for PDF map visualization, namely the map part in the PDF map, and the other part of the graphical objects is simultaneously associated with attribute information and is used for geographic element query, namely the geographic information part in the PDF map. The PDF tile map pyramid model specifies tile grading rules of the Web mercator projection PDF map with five scales of 1:100 ten, 1:25 ten, 1:5 ten, 1:1 ten and 1:2 thousand, calculates a tile coordinate list covered by a map width range of a Web mercator projection PDF map file with any scale, and cuts the Web mercator projection PDF map by using an area where the tile belongs to obtain the PDF tile map. The specific process is as follows:
(1) the method comprises the following steps of acquiring a map scale and a map range by using a PDF map object, and calculating and returning a tile coordinate list covered by the map range, wherein the specific process comprises the following steps:
firstly, acquiring a map scale K of a Web mercator projection PDF map, and acquiring a PDF tile map level Z according to a table 1, wherein the PDF tile map level is 3 if the map scale is 1: 50000;
acquiring the projection coordinates of the Web mercator in the picture range of the PDF map projected by the Web mercator, and the left lower corner point (x)LB,yLB) Right upper corner point (x)RT,yRT)；
(x) calculation using equation 2LB,yLB)、(xRT,yRT) Tile coordinate at level Z (X)LB,YLB)、(XRT,YRT)；
Fourthly, returning the tile coordinate list { (X, Y) | XLB≤X≤XRT，YLB≤Y≤YRT}。
(2) And based on the tile coordinate list, utilizing a PDF page cutting technology to cut the graphic objects in the PDF map page.
For any tile coordinate (X, Y) in the tile list at level Z, compute the Web mercator projection coordinates of the tile rectangle: left lower corner (d × X, d × Y), right upper corner (d × (X +1), d × (Y + 1)). Calculating user coordinates of tile rectangles within the PDF map page using spatial reference objects in the PDF map object: lower left corner (Ux)1,Uy1) Right upper corner point (Ux)2,Uy2). The tile rectangle extension σ is 0.567 to obtain a cropping rectangle R (R) for cropping the graphic object in the PDF map pageleft，Rbottom，Rright，Rtop) I.e. { Rleft＝Ux1-σ，Rbottom＝Uy1-σ，Rright＝Ux2+σ，Rtop＝Uy2+σ}。
Based on the related parameters of the PDF tile map corresponding to the tile coordinates (Z, X, Y) calculated above, a PDF tile map object is created by using a PDF map parser, and the following settings are carried out:
setting the page size as follows: wide Ux2-Ux1High Uy2-Uy1；
Initializing a spatial reference object in the PDF tile map object by using the spatial reference object in the PDF map object;
thirdly, setting transformation matrix parameters [ a b c d e f ] in space reference nodes of PDF tile map]The values of e and f in (1) are respectively: ux1、Uy1。
Five types of graphic objects are mainly included in the PDF map page, which are respectively: text object (Text), Path object (Path), inline Image object (Image), shadow object (Shading), and extrinsic object (XObject). Acquiring all the graphic objects by using the page objects of the PDF map object, acquiring the external rectangle of each graphic object, judging the position relation between the external rectangle and the cutting rectangle, and performing the following operations:
if the circumscribed rectangle is outside the cutting rectangle, the graphic object is outside the PDF tile map and is not processed;
if the external rectangle is in the cutting rectangle or is intersected, the graphic object is positioned in the PDF tile map, the graphic object is copied to a PDF map page in the PDF tile map object, and the point coordinate in the graphic object is transformed into the lower left corner point (Ux) of the tile rectangle1，Uy1) If the attribute information is associated with the graphic object, the attribute information associated with the graphic object is added to the PDF map page in the PDF tile map object and the graphic object is associated with the PDF map page in the PDF tile map object.
And when all the graphic objects in the PDF tile map page are processed, updating the PDF document structure tree in the PDF tile map object. And constructing a PDF tile map file name named by the tile coordinate information, creating a PDF file by using the file name, saving and outputting the PDF tile map file to the newly created PDF file by using a PDF tile map object, and obtaining the cut PDF tile map file.
Generally, graphic objects in a PDF page are mainly path objects, a path is composed of a plurality of straight line segments and a cubic bezier curve, and the path can be used for drawing lines and determining the shape of a region to be filled. When the circumscribed rectangle and the clipping rectangle of the path object intersect, preferably, when the graphic object has no associated attribute information, the invention provides a method for performing vector clipping processing on the path in the graphic object by using the clipping rectangle, which comprises the following specific processes:
if the path only consists of a plurality of straight line segments, namely a broken line or a polygon, broken line cutting and polygon cutting are realized by adopting a classical algorithm, such as a Cyus-Beck line cutting algorithm, a Liang-Bar-sky line cutting algorithm, a Nichol-Lee-Nichol line cutting algorithm, a Weiler-Atherton polygon cutting algorithm, a Sutherland-Hodgeman polygon cutting algorithm and the like. Examples of clipping for polylines and polygons are shown in FIG. 5: in the diagram (a), starting from a starting point A, calculating an entry point 1, an entry point 3 and an entry point 5 of a path broken line entering a cutting rectangular area and an exit point 2 and an exit point 4 leaving the cutting rectangular area along the direction of the path broken line, when constructing a path after cutting, setting an entry point operator as'm' and an exit point operator as 'l', reserving a part between the adjacent entry point and the adjacent exit point, if the starting point is in the cutting rectangular area, taking the starting point as a first entry point, and if the end point is in the cutting rectangular area, taking the end point as a last exit point, and obtaining a path after cutting '1-2, 3-C-4, 5-E'; in the diagram (b), starting from the starting point A, the entering points 2 and 4 of the polygon edge into the cutting rectangular area and the exiting points 1 and 3 leaving the cutting rectangular area are obtained along the direction of the path broken line, if the starting point is in the cutting rectangular area, the starting point is taken as a first entering point, the first entering point is taken as the starting point, one entering point and one exiting point are taken as a group along the direction of the path broken line, and the nodes in the middle of the entering point and the exiting point are reserved to form a polygon, such as 'A-1-2-D-3-4-A'.
If the path is composed of the cubic bezier curve or is composed of a straight line segment and the cubic bezier curve in a mixed mode, the path cutting processing is carried out by taking the cubic bezier curve as a unit under the condition that the intersection point of the cubic bezier curve and the cutting rectangle is not calculated specifically. As shown in fig. 6, the path in the diagram (a) is composed of a straight line segment and cubic bezier curve elements 1, 2,3, and 4 from the starting point a. Firstly, extracting the starting point and the ending point and the control point of any cubic bezier curve unit in the path, such as 1, calculating the circumscribed rectangles of the starting point and the ending point, such as the circumscribed rectangle is in the cutting rectangle area, keeping the cubic bezier curve unit, such as the circumscribed rectangle is outside the cutting rectangle area, discarding the cubic bezier curve unit, and connecting the starting point and the ending point by a straight line segment, wherein in the graph (b), 1, 2,3, 4 are kept. Then, from the starting point A, along the path direction, the entry points 1 and 3 where the path enters the cutting rectangular region in a straight line and the exit point 2 where the path leaves the cutting rectangular region in a straight line are obtained, and if the end point of the remaining cubic bezier curve unit is outside the cutting rectangular region and the next segment thereof is a straight line segment, the end point of the cubic bezier curve unit is taken as the exit point, if the starting point is inside the cutting rectangular region, the starting point is taken as the first entry point, and if the end point is inside the cutting rectangular region, the end point is taken as the last exit point. Finally, the in-point operator is set to "m", the out-point operator is set to "l", and the part between the adjacent in-point and out-point is reserved, resulting in the clipped path "1-S1-S2-2, 3-E".
And 4, step 4: and acquiring and splicing PDF tile maps with the same tile coordinates obtained by cutting adjacent map sheets.
Because the primitive contents in the PDF tile map may come from two or four adjacent PDF maps, the PDF tile maps with the same tile coordinates obtained by clipping the adjacent PDF tile maps in step 3 all only include a part of graphics. As shown in fig. 7, there are 4 PDF tile map files with the same tile coordinate at level 3, which need to be stitched to obtain a complete PDF tile map, and the specific process is as follows:
extracting PDF tile map files with the same tile coordinates under the same map level, wherein the number of the files is more than 1, and storing the files into a file list;
analyzing a first PDF tile map file in the file list by using a PDF map analyzer to obtain a target PDF map object;
analyzing the next PDF tile map file in the file list by using a PDF map analyzer to obtain a source PDF map object;
acquiring all the graphic objects by utilizing the page objects of the source PDF map object, sequentially copying each graphic object into the page object of the target PDF map object, copying the associated attribute information into the page object of the target PDF map object if the graphic object has the associated attribute information, and deleting the source PDF map object and the corresponding PDF tile map file after the copying is successful;
and fifthly, if the number of the files in the file list is larger than 2, repeating the third step and the fourth step, updating the page object of the target PDF map object, and outputting and replacing the PDF file corresponding to the target PDF map object by using the target PDF map object to obtain the spliced PDF tile map.
The invention is not limited to the examples, and any equivalent changes to the technical solution of the invention by a person skilled in the art after reading the description of the invention are covered by the claims of the invention.

Claims (5)

  1. The method for manufacturing the PDF tile map is characterized by comprising the following steps:
    the manufacturing method of the PDF tile map is realized by the following steps:
    the method comprises the following steps of adopting a tile pyramid model to store a PDF map in a blocking mode in a PDF format, firstly establishing the PDF tile map pyramid model, then converting other projected PDF maps into a Web mercator projected PDF map through projection, finally cutting the Web mercator projected PDF map based on the PDF tile map pyramid model, splicing the PDF tile maps with the same tile coordinates, and finally obtaining the PDF tile map:
    the method specifically comprises the following steps:
    step 1: establishing a PDF tile map pyramid model, which specifically comprises the following steps:
    (1) establishing a Web mercator projection coordinate transformation object;
    (2) dividing the pyramid level of the PDF tile map, and converting the Web mercator projection coordinates into user coordinates of the PDF tile map corresponding to tile coordinates under a certain level Z in the pyramid level;
    step 2: the PDF map projective transformation is a Web mercator projection, and specifically comprises the following steps:
    (1) analyzing the Gaussian projection PDF map file by using a PDF map analyzer to obtain a Gaussian projection PDF map object;
    (2) establishing a coordinate transformation model of the Gaussian projection PDF map to the Web mercator projection PDF map;
    (3) extracting all graphic objects in a PDF map page, and performing coordinate transformation on point coordinates in the graphic objects by using a coordinate transformation model;
    (4) setting page size, map projection parameters and transformation matrix parameters, and storing a Web mercator projection PDF map file;
    and step 3: cutting the Web mercator projection PDF map based on the PDF tile map pyramid model, and specifically comprises the following steps:
    (1) obtaining a map scale and a map frame range by using a PDF map object, and calculating and returning a tile coordinate list covered by the map frame range;
    (2) based on the tile coordinate list, cutting the graphic objects in the PDF map page by using a PDF page cutting technology;
    and 4, step 4: and acquiring and splicing PDF tile maps with the same tile coordinates obtained by cutting adjacent map sheets.
  2. 2. The method of making a PDF tile map according to claim 1, wherein:
    the step 1(1) is to establish a Web mercator projection coordinate transformation object, and is specifically realized by the following steps:
    the PDF tile map pyramid model takes a square area, so, when the Mexico Kanto projection is adopted, the earth is regarded as a sphere, the equator is taken as a standard latitude line, the initial meridian is taken as a central meridian, the intersection point of the two is the origin of coordinates, the east is the X-axis forward direction, the north is the Y-axis forward direction, and the projection formula is shown as formula 1:
    Figure FDA0002962823030000021
    wherein:
    r6378137 meters, i.e. radius of the earth;
    λ -longitude in radians;
    Figure FDA0002962823030000031
    -latitude in radians;
    the step 1(2) is to divide the pyramid level of the PDF tile map, and transform the Web mercator projection coordinates into user coordinates of the PDF tile map corresponding to tile coordinates at a certain level Z in the pyramid level, and is specifically realized by the following steps:
    the PDF tile map adopts Web mercator projection, the map range is a square area, and the side length is as follows: 40075016.686 meters, latitude range: -85.05 ° to 85.05 °, longitude range: -180 ° to 180 °;
    the tile blocking specifically comprises:
    dividing map range into 4 equal parts9The block is used as the level 1 of the PDF tile map, and the corresponding map scale is 1:100 ten thousand;
    2, each block of the 1 st stage is equally divided into 42The block is used as the level 2 of the PDF tile map, and the corresponding map scale is 1:25 ten thousand;
    3 equally dividing each block of the 2 nd level into 43The block is used as the 3 rd level of the PDF tile map, and the corresponding map scale is 1:5 ten thousand;
    fourthly, each block of the 3 rd level is equally divided into 42The block is used as the 4 th level of the PDF tile map, and the corresponding map scale is 1:1 ten thousand;
    equally dividing each block of the 4 th level into 42A block, as level 5 of the PDF tile map, with a corresponding map scale of 1:2 k;
    the tile coordinate origin of the PDF tile map is at a position where the longitude and latitude are both 0, with the lower left corner of the PDF tile as a reference point, tile coordinates (Z, X, Y), where: z is PDF tile map level, 1-5 levels in total; x, Y are integers, starting with 0; x is horizontal, Y is vertical, the origin of coordinates is positive upwards and rightwards, and negative downwards and leftwards, namely the east longitude X takes a positive value, the west longitude X takes a negative value, the north latitude Y takes a positive value, and the south latitude Y takes a negative value;
    PDF tile map coordinate transformation: the longitude and latitude coordinates and the Web mercator projection coordinates are directly transformed by a formula 1 and are irrelevant to the level of the PDF tile map; the Web mercator projection coordinates are converted into tile coordinates and user coordinates at a certain PDF tile map level;
    the Web mercator projection coordinates (X, Y) are transformed into tile coordinates (X, Y) at a certain level Z, as shown in equation 2:
    Figure FDA0002962823030000041
    in the formula, R is the earth radius, d is the tile side length, and INT represents rounding the numerical value in brackets, namely, rounding off the part behind a decimal point;
    the Web mercator projection coordinates (X, Y) are transformed into user coordinates (U) of the PDF tile map corresponding to tile coordinates (X, Y) at a certain level Zx,Uy) As shown in equation 3:
    Figure FDA0002962823030000042
    in the formula (I), the compound is shown in the specification,
    Figure FDA0002962823030000043
    k is the map scale denominator at a certain level Z.
  3. 3. The method of making a PDF tile map according to claim 1, wherein:
    the step 2(1) is to analyze the gaussian projection PDF map file by using a PDF map analyzer to obtain a gaussian projection PDF map object, and is specifically realized by the following steps:
    the PDF map object comprises a PDF document structure tree object and a PDF map space reference object, the PDF document structure tree mainly comprises PDF map page nodes, and the PDF map space reference mainly realizes the purpose of converting the user coordinates of the graphic object in the page into projection coordinates and longitude and latitude coordinates;
    the step 2(2) is to establish a coordinate transformation model of the gaussian projection PDF map to the Web mercator projection PDF map, and is specifically realized by the following steps:
    for gaussian projection PDF maps, with PDF map objects: firstly, acquiring a Gaussian projection PDF map scale of 1: K; acquiring geographical longitude and latitude of map range of Gaussian projection PDF map, namely longitude and latitude coordinates of left lower corner of inner outline
    Figure FDA0002962823030000051
    Longitude and latitude coordinates of upper right corner
    Figure FDA0002962823030000052
    Thirdly, the longitude and latitude coordinates are calculated by the formula 1
    Figure FDA0002962823030000053
    Conversion to Web mercator projection coordinates (x)1,y1)、(x2,y2)；
    In the process of transforming the Gaussian projection PDF map into the Web mercator projection PDF map, eliminating the graphic object outside the inner outline, only transforming the graphic object within the map breadth range, and taking the inner outline rectangle as the page rectangle of the transformed Web mercator projection PDF map; establishing a user coordinate transformation formula for projecting the PDF map to the Web mercator by the Web mercator projection coordinates, wherein the user coordinate transformation formula is shown as a formula 4:
    Figure FDA0002962823030000054
    in the formula (I), the compound is shown in the specification,
    Figure FDA0002962823030000055
    k is a map scale denominator;
    the width of the page rectangle of the Web mercator projection PDF map is as follows:
    Figure FDA0002962823030000056
    the height is:
    Figure FDA0002962823030000057
    the step 2(3) extracts all the graphic objects in the PDF map page, and performs coordinate transformation on the point coordinates in the graphic objects by using a coordinate transformation model, which is specifically realized by the following steps:
    traversing all the graphic objects in the content stream under the page node, acquiring the user coordinates of all the points of each graphic object aiming at each graphic object, and performing the following processing:
    converting user coordinates into longitude and latitude coordinates by using PDF map space reference;
    converting the longitude and latitude coordinates into Web mercator projection coordinates;
    thirdly, transforming the Web mercator projection coordinate into a user coordinate after coordinate transformation;
    replacing the user coordinate before coordinate transformation with the user coordinate after point coordinate transformation in the graphic object;
    updating the content flow of the PDF map page when the point coordinates of all the graphic objects in the page are converted;
    the step 2(4) is to set the page size, the map projection parameters and the transformation matrix parameters, and store the Web mercator projection PDF map file, and is specifically realized by the following steps:
    setting the size of a Web mercator projection PDF map Page (Page) and the width as follows:
    Figure FDA0002962823030000061
    the height is:
    Figure FDA0002962823030000062
    secondly, setting map projection parameters in the space reference nodes under the page as Web mercator projection, wherein the specific parameters are as follows:
    type (2):
    WGS_1984_Web_Mercator_Auxiliary_Sphere；
    parameters are as follows:
    PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION[“Mercator_Auxiliary_Sphere”],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",0.0],PARAMETER["Standard_Parallel_1",0.0],PARAMETER["Auxiliary_Sphere_Type",0.0],UNIT["Meter",1.0],AUTHORITY[“EPSG”,3857]]；
    thirdly, setting transformation matrix parameters [ a b c d e f ] in space reference nodes under the page]Is [ s 00 s x ]1 y1]；
    And fourthly, updating the PDF document structure tree, and saving the PDF map object into the new PDF file to obtain the Web mercator projection PDF map file.
  4. 4. The method of making a PDF tile map according to claim 1, wherein:
    the step 3(1) is to obtain a map scale and a map range by using the PDF map object, calculate and return a tile coordinate list covered by the map range, and is specifically realized by the following steps:
    acquiring a map scale K and PDF tile map level of a Web mercator projection PDF map;
    obtaining the projection coordinates of the Web mercator in the picture range of the PDF map projected by the Web mercator, and the lower left corner point (x)LB,yLB) Right upper corner point (x)RT,yRT)；
    Calculating (x)LB,yLB)、(xRT,yRT) Tile coordinates (X) at acquisition levelLB,YLB)、(XRT,YRT)；
    Fourthly, returning the tile coordinate list { (X, Y) | XLB≤X≤XRT,YLB≤Y≤YRT}；
    The step 3(2) is to perform cutting processing on the graphic object in the PDF map page by using a PDF page cutting technology based on the tile coordinate list, and is specifically realized by the following steps:
    calculating user coordinates of a tile rectangle corresponding to tile coordinates (X, Y) under level Z in a PDF map page: lower left corner (Ux)1,Uy1) Right upper corner point (Ux)2,Uy2) The tile rectangle is expanded by 0.567 to obtain a clipping rectangle R (R)left,Rbottom,Rright,Rtop) For graphic objects within a PDF map page: if the circumscribed rectangle is outside the cutting rectangle, no processing is carried out; if the bounding rectangle is within or intersects the cropping rectangle, copying the graphical object into a PDF map page in a PDF tiled map object and transforming the point coordinates in the graphical object to the lower left corner point (Ux) of the tiled rectangle1,Uy1) If the graphic object is associated with the attribute information, adding the attribute information associated with the graphic object into a PDF map page in the PDF tile map object, and simultaneously associating the graphic object in the PDF map page in the PDF tile map object;
    if the graphic object is a path object and the attribute information is not associated, preferably, when the circumscribed rectangle and the clipping rectangle are intersected, performing vector clipping processing on the path by using the clipping rectangle: if the path only consists of a plurality of straight line segments, namely a broken line or a polygon, the broken line cutting and the polygon cutting are realized by adopting a classical algorithm; if the path is composed of the cubic bezier curve or is composed of a straight line segment and the cubic bezier curve in a mixed mode, the path cutting processing is carried out by taking the cubic bezier curve as a unit under the condition that the intersection point of the cubic bezier curve and the cutting rectangle is not specifically calculated.
  5. 5. The method of making a PDF tile map according to claim 1, wherein:
    step 4, obtaining and splicing the PDF tile maps with the same tile coordinates obtained by cutting adjacent map sheets, which is specifically realized by the following steps:
    extracting PDF tile map files with the same tile coordinates under the same map level, wherein the number of the files is more than 1, and storing the files into a file list;
    analyzing a first PDF tile map file in the file list by using a PDF map analyzer to obtain a target PDF map object;
    analyzing the next PDF tile map file in the file list by using a PDF map analyzer to obtain a source PDF map object;
    acquiring all the graphic objects by utilizing the page objects of the source PDF map object, sequentially copying each graphic object into the page object of the target PDF map object, copying the associated attribute information into the page object of the target PDF map object if the graphic object has the associated attribute information, and deleting the source PDF map object and the corresponding PDF tile map file after the copying is successful;
    and fifthly, if the number of the files in the file list is larger than 2, repeating the third step and the fourth step, updating the page object of the target PDF map object, and outputting and replacing the PDF file corresponding to the target PDF map object by using the target PDF map object to obtain the spliced PDF tile map.
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